Variable resistance control



P 1957 J. D. VAN BENTHUYSEN ETAL 3,34l,799

VARIABLE RESISTANCE CONTROL Filed Feb. 24, 1965 2 Sheets-Sheet 1 llb/l|c FIGURE 2.

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VARIABLE RES I STANCE CONTROL Filed Feb. 24, 1965 2 Sheets-Sheet 2 Fl GURE 6.

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INVENTORS JO HN D. VAN BENTHUYSEN WILBERT F/lgBUDD BY @13 4 AT ORNEYUnited States Patent 3,341,799 VARIABLE RESISTANCE CONTROL John D. VanBenthuysen and Wilbert H. Budd, Ellrhart, Ind., assignors to CTSCorporation, Elkhart, Ind., a corporation of Indiana Filed Feb. 24,1965, Ser. No. 434,891 7 Claims. (Cl. 338-480) ABSTRACT OF THEDISCLOSURE A rectilinear variable resistance control in a housingemploying a lead screw drivably engaging a contact assembly having acontact wipably engaging a resistance element. A clutch assembly havinga first cylindrical member integral with the lead screw, a secondcylindrical member connected to a rotatable member extending outwardlyof the housing and a resilient member biasing the cylindrical membersinto engagement prevents damage to the control.

The present invention relates to variable resistance controls, and, moreparticularly, to a rectilinear variable resistance control.

Rectilinear variable resistance controls have been advantageouslyemployed wherever a compact control is necessary with a fine degree ofadjustment. The operating member of such controls, i.e., a contactassembly, is generally enclosed in a housing, and it is diificult todetermine when the contact assembly has reached the end of its travel ineither direction. Clutches for limiting the travel of the contactassembly in variable resistance controls are available on the market butare inadequte for use in controls having a minimum housing length. Itwould, therefore, be desirable to provide a rectilinear variableresistance control with an improved clutch assembly of a short axialdistance for preventing damage to the control when an operator continuesto adjust the control after the contact assembly has reached the end ofits travel in either direction.

In the manufacture of rectilinear variable resistance controls, it isnecessary that chucking action between the contact arm of a contactorand the lead screw be kept to a minimum. Various constructions on themarket have received a certain degree of acceptance, however, a certainamount of free play exists and becomes apparent when the rotation of thelead screw is reversed. It would, therefore, be desirable to provide avariable resistance control having the contactor fixedly secured to thedrive block.

One of the factors determining the wattage rating of a variableresistance control is the ability of the resistance element to dissipateheat rapidly. Generally this is no probhim since the size of theresistance element can be increased to accommodate the necessary wattagerating. However, when the size of the resistance element is limited, itis necessary that other means be employed for dissipating the heat ofthe resistance element. It would, therefore, also be desirable toprovide a rectilinear variable resistance control employing a resistanceelement having means for dissipating heat rapidly.

Many variable resistance controls are exposed to atmospheric conditionsinjurious to the operable members of the control. In an efiort to sealsuch controls and still maintain flush walls for stacking the controls acover closing the housing is provided with a peripheral groove extendingalong the junction between the housing and the cover, and bondingmaterial is disposed in the groove for securing the cover to thehousing.

Accordingly, it is an object of the present invention to provide animproved variable resistance control.

An additional object of the present invention is to provide a variableresistance control having a clutch assembly electrically insulating alead screw from a rotatable member.

A further object of the present invention is to provide a variableresistance control having a contactor welded to a drive block ofelectrically conductable material threadedly engaging a rotatable leadscrew.

Still. an additional object of the present invention is to provide agroove extending at least partially along a junc' tion formed by ahousing and a cover of a variable resistance housing with bondingmaterial disposed in the groove for sealing the cover to the housing.

Still another object of the present invention is to pro vide a variableresistance control having a wirewound resistance element having amandrel of high thermal conductivity.

A still further object of the present invention is to provide arectilinear variable resistance control with a clutch assembly having apair of cylindrical members having a high diameter to thickness ratio.

Further objects and advantages of the present invention will becomeapparent as the following description proceeds, and the features ofnovelty characterizing the invention will be pointed out withparticularity in the claims annexed to and forming a part of thisspecification.

Briefly, the present invention is concerned with a variable resistancecontrol having a housing provided with a cavity opening to one sidethereof receiving a resistance element, a lead screw, a contact assemblyfor wiping contact with the resistance element and a clutch assembly fordisengaging the lead screw from a rotatable member when the contactassembly reaches the end of its travel in either direction in thehousing. The clutch assembly comprises a first cylindrical memberintegral with the lead screw, a second cylindrical member connected tothe rotatable member and a resilient member biasing the cylindricalmembers into engagement. In one embodiment of the invention, the contactassembly comprises a drive block of electrically conductable materialthreadedly engaging the lead screw and having a contactor welded to thedrive block. Insulating means such as an electrically insulatable secondcylindrical member is employed between the lead screw and the rotatablemember. A cover closes the cavity or open side of the housing and aperipheral groove extending at least partially around the junctionbetween the housing and the cover is filled with a bonding materialsecuring the cover to the housing thereby providing flush outer sidesfor the housing. Tubular members projecting from the housing arereceived in apertures provided in the cover.

For a better understanding of the present invention, reference may behad to the accompanying drawings wherein the same reference numeralshave been applied to like parts and wherein:

FIGURE 1 is an isometric view of the variable resistance control made inaccord with the present invention;

FIGURE 2 is an end view of the control shown in FIGURE 1;

FIGURE 3 is a side elevational view of the control of FIGURE 1 with thecover removed;

FIGURE 4 is a sectional view taken along line IVIV of FIGURE 3, assumingthat FIGURE 3 is shown in full;

FIGURE 5 is an end view of the control similar to FIGURE 2 except thatthe cover is not fixedly secured to the housing;

FIGURE 6 is an exploded view of the control of FIG- URE 1;

FIGURE 7 is an isometric view of the contactor shown in FIGURES 3 and 6of the drawings; and

FIGURE 8 is a fragmentary section of another embodiment of a clutchassembly employed in the present invention.

Referring now to the drawings, there is illustrated a variableresistance control, generally indicated at 10, comprising a housing 11having a bottom wall 11a, side walls 11b and 11c, a top wall 11d and endwalls 11:: and 11] defining a hollow interior or cavity 12. The housing11 is provided with a pair of transverse openings 13 to facilitatemounting of the control 10. The openings 13 are partially defined by apair of tubular members 14 (see FIGURE 6) projecting outwardly of thehousing adjacent to the cavity 12. A cover 15 provided with a pair oftransverse apertures 16 closes the cavity 12 of the housing 11, and thetubular members 14 positioned in the apertures 16 of the cover 15 alignthe cover with the housing. The outer surface of the cover 15 definesone of the side walls 11b of the housing. The cover 15 and the housing11 are preferably molded from a suitable molding resin such as phenolcondensation composition or a methacrylate resin. For the purpose ofmaintaining flush exterior walls for the housing to facilitate stackingthereof, a peripheral groove 17 extends at least partially around thejunction 18 between the housing 11 and the cover 15 as best shown inFIGURES 4 and 5 of the drawings. A suitable epoxy bonding material 19 isdeposited in the groove and, upon solidification of the bondingmaterial, the cover is fixedly secured to the housing without having anybonding material above the surface of the walls of the housing. Thegroove 17 also provides a suitable space for the bonding material 19after the cover is assembled to the housing thereby eliminating any harmwhich could result if the bonding material 19 were applied to the edgesof the housing and the cover before assembly and some of the bondingmaterial 19 contacted one of the operating members in the housing.

Preferably and as best shown in FIGURE 3 of the drawings, a meansdefining a resistance path 20 is mounted in the lower portion of thecavity 12 intermediate the transverse openings 13. The means definingthe resistance path 20 can be a wirewound element, a carbon element or aglass frit resistance element deposited on an electricallynonconductable substrate such as steatite. In the embodiment shown inthe drawings, the resistance element is a wirewound element preferablycomprising a solid electrically conductable mandrel 21 of suitablematerial, such as copper, and a layer of insulation coats the outersurface of the mandrel for insulating a coiled helical resistance wire22 wound thereon. One end 22a of the resistance wire 22 is connected tothe solid electrically conductable mandrel 21 and the other end 22b ofthe resistance wire is connected to a suitable terminal lead 23. Anotherterminal lead 24 is connected to the mandrel 21 thereby including themandrel as a conductive portion of a circuit and also eliminating theneed for a longer terminal lead to the other end 22a of the resistanceeslement 22. Since a metal such as copper is a good thermally conductivematerial, the heat generated by the resistance element is rapidlyabsorbed and dissipated by the mandrel 21.

In order to wipe a contactor 25 intermediate the ends of the resistancepath 20, a lead screw 26 is rotatably mounted in the housing. Thehousing 11 is provided with a pair of arcuate bearing surfaces 27 and 28rotatably supporting the ends of the lead screw 26. The end 26a of thelead screw 26 is supported by the bearing surface 27 and has a diametersubstantially the same as the threaded portion of the lead screw. Theother end of the lead screw 26 is defined by a cylindrical membre 29supported by the bearing surface 28, the diameter of the cylindricalmember 29 being substantially larger than the threaded portion of thelead screw. A contact assembly operably connected to the lead screw 26comprises an electrically conductable drive block 30 threadedly engagingthe lead screw 26. The contactor 25 is preferably fixedly secured to thedrive block 30 by spot welding thereby eliminating any free playtherebetween. A C- washer 26b disposed in the slot 260 adjacent to theend 26a limits travel of the drive block 30* on the lead screw in onedirection. For the purpose of electrically connecting the contactor toan electrical circuit, a collector 31, is suitably mounted in the cavityof the housing. The collector 31 is of U-shaped construction, the bightportion of the U being in contact with the contactor 25, the legs of theU being disposed in suitable slots forming part of the cavity 12 of thehousing 11. A terminal lead 31a is connected to one of the legs of thecollector 31. The contactor 25 is provided with a contact arm 25a forwiping contact with the resistance path 20 and a collector arm 25b forwiping contact with the collector 31.

Preferably and in accord with the present invention, a clutch assembly32 interposed between the externally rotatably means defined by aslotted shaft 33 and the lead screw 26 prevents damage to the housing orto the threaded portion of the lead screw and the internal thread of thedrive block 30 when the contact assembly, i.e., the drive block 30 andthe contactor 25, reaches the end of its travel in either directionalong the resistance path. The clutch assembly 32 comprises a pair ofcylindrical members 29 and 34 of the same diameter, the firstcylindrical member 29 also functioning as the bearing for one end of thelead screw. The second cylindrical member 34 integral with the rotatablemeans 33 is rotatably supported by the bearing surface 28 therebyremaining in proper alignment with the first cylindrical member. It iscritical that the ratio of the diameter of each of the cylindricalmembers 29 and 34 to the diameter of the lead screw be substantiallygreater than 1:21. In a control made in accord with the presentinvention, the diameter of the cylindrical members was .124 inch and thediameter of the lead screw was .058 inch resulting'in a ratio of 2.2:1.Each of the cylindrical members 29 and 34 is provided with a clutch face29a and 34a respectively, and a resilient means, e.g., a tension sealingwasher 36, circumposing the rotatable means 33 biases the clutch facesinto engagement thereby connecting the rotatable means 33 to the leadscrew 26. For the purpose of maintaining a positive drive between therotatable means 33 and the lead screw 26 when the rotatable means drivesthe lead screw and the contactor 25 is intermediate the ends of theresistance path 20, the clutch face 25a of the first cylindrical member29 is provided with a groove 2% and the clutch face 35a of the secondcylindrical member 34 is provided with an elongated bead 34b disposed inthe groove 29a. Thus any torque applied to the rotatable means 33 istransferred to the lead screw 26 and, when the drive block 30 reachesthe end of its travel in either direction, the lead screw encounterssubstantial resistance to rotation causing the clutch faces 29a and 34ato rotate relative to each other, thereby preventing damage to anyportion of the control 10.

It will be appreciated that when the drive block 30 is of anelectrically conductable material the current is transmitted from thecontactor 25 to the lead screw 26.

It is, therefore, necessary that some means be employed for electricallyinsulating the rotatable means 33 from an electrically conducting leadscrew 26. To this end, the rotatable means 33 is, preferably, of anelectrically nonconductable material. It is to be understood, however,that if the rotatable means is of similar electrically conductablematerial such as the lead screw, an electrically insulatable clutch disc37 is interposed between the clutch faces as shown in FIGURE 8 of thedrawings. The external portion of the rotatable means 33 can be slottedfor receiving a suitable tool, such as a screwdriver. As best seen inFIGURE 4 of the drawing, an inwardly extending projection 15a integralwith the cover engages and maintains the one end 26a of the lead screw26 against the bearing surface.

In order to secure the terminal leads 23, 24 and 31a extending outwardlyof the housing 11, the housing is provided with a slot 38 and a pair ofposts 39 extend outwardly from one of the walls of the slot providingthree passageways, the terminal leads 23, 24 and 31a being disposed inthe passageways. An inwardly turned member 15b integral with the cover15 and disposed in the slot 38 secures the terminal leads in thehousing.

While there has been illustrated and described what is at presentconsidered to be a preferred embodiment of the present invention, and asingle modification thereof, it will be appreciated that numerouschanges and modifications are likely to occur to those skilled in theart, and it is intended in the appended claims to cover all thosechanges and modifications which fall within the true spirit and scope ofthe present invention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. In a variable resistance control having a housing, a resistanceelement disposed in the housing, a lead screw rotatably journaled in thehousing, a contactor for making wiping contact with the resistanceelement, and means connecting the contactor to the lead screw for movingthe contactor intermediate the ends of the resistance element as thelead screw is rotated the improvement comprising a pair of engagingmembers having clutch faces, one of the engaging members being drivinglyconnected to the lead screw, the other of the engaging members beingrotatable externally of the housing, and electrically nonconductingresilient means biasing one of the engaging members into drivingengagement with the other engaging member.

2. In a variable resistance control having a housing, a resistanceelement disposed in the housing, a lead screw rotatably journaled in thehousing, a contactor for making wiping contact with the resistanceelement, and means drivingly connecting the contactor to the lead screwfor shifting the contactor intermediate the ends of the resistanceelement as the lead screw is rotated the improvement comprising a firstmeans defining a clutch face integral with the lead screw and normal tothe axis thereof, a rotatable means extending outwardly of the housing,a second means defining a clutch face drivingly connected to therotatable means, a projection carried by one of the clutch faces, theother clutch face being provided with a recess receiving the projection,and electrically nonconductive resilient means biasing one of the clutchfaces into driving engagement with the other clutch face.

3. In a variable resistance control the combination of a housing, meansdefining a resistance path disposed in the housing, a lead screwrotatably journaled in the housing, contact means engaging theresistance path, the contact means being drivingly connected to the leadscrew for shifting the contact means intermediate the ends of theresistance path, a shaft extending outwardly of the housing, clutchmeans drivingly connecting the shaft to the lead screw, and electricallynonconducting resilient means sealing the inside of the housing aroundthe shaft, said resilient means also biasing the shaft against the leadscrew thereby enabling the shaft and lead screw to rotate as a unituntil the contact means reaches one of the ends of the resistance path.

4. In a variable resistance control the combination of an elongatedhousing provided with a cavity, means defining a resistance pathdisposed in the cavity of the housing, a lead screw rotatably journaledin the housing in spaced parallel relationship to the means defining theresistance path, a contact assembly driven by the lead screw for makingwiping contact with the resistance path intermediate the ends thereof,rotatable means extending outwardly of the housing, a first cylindricalmember provided with a clutch face and integral with the lead screw, 21second cylindrical member provided with a clutch face and integral withthe rotatable means, the clutch faces being normal to the axis of thelead screw, one of the clutch faces being provided with an elongatedgroove, the other clutch face being provided with an elongated beaddisposed in the elongated groove, and resilient means comprising anO-ring circumposing the rotatable means, said resilient means biasingthe clutch faces together for connecting the rotatable means to the leadscrew whereby upon rotating the contact assembly to one of the ends ofthe resistance path relative rotation between the clutch faces willoccur.

5. A variable resistance control comprising a housing of electricallynonconductable material, a resistance element disposed in the housing, apair of terminal leads connected to the ends of the resistance element,a lead screw rotatably mounted in the housing in spaced relationship tothe resistance element, an electrically conductable internally threadeddrive block threadedly engaging the lead screw, a collector, acontractor secured to the drive block for making wiping contact with theresistance element and the collector intermediate the ends thereof, arotatable means projecting outwardly of the housing, means insulatingthe rotatable means from the lead screw, a first cylindrical memberintegral with the lead screw, a second cylindrical member connected tothe rotatable means, one of the cylindrical members being provided witha groove, the other cylindrical member being provided with a projectiondisposed in the groove, and an O-ring biasing the cylindrical membersinto engagement with each other whereby upon rotation of the rotatablemeans the lead screw rotates with the rotatable means until thecontactor reaches one of the ends of the resistance element.

6. A variable resistance control comprising a housing having a cavity,means defining a resistance path disposed in the cavity of the housing,a lead screw rotatably journaled in the housing in spaced parallelrelationship to the resistance path, a contact assembly operablyconnected to the lead screw for making wiping contact with theresistance path, a pair of tubular members projecting laterally of thehousing, a cover provided with a pair of spaced apertures closing thecavity of the housing, the tubular members being received in theapertures of the cover, the housing being provided with an end portion,the end portion of the housing being provided with a slot, a pluralityof terminal leads connected to the means defining the resistance pathand to the contact assembly and disposed in the slot, and an inwardlyturned end portion integral with the cover engaging the terminal leadsand fixedly securing the terminal leads in the slot.

7. In a variable resistance control the combination of a housingprovided with a cavity, a resistance element disposed in the cavity ofthe housing, a lead screw rotatably journaled in the housing, a contactassembly for making wiping contact with the resistance element anddrivingly connected to the lead screw, a first cylindrical memberintegral with the lead screw having a clutch face normal to the axis ofthe lead screw, the housing being provided with a bearing surfacesupporting the cylindrical member, rotatable means extending outwardlyof the housing, a second cylindrical member integral with the rotatablemeans and having a clutch face normal to the axis of rotati-0n of saidrotatable means, the second cylindrical memher being supported by thebearing surface, a clutch disc interposed between the cylindricalmembers, and a resilient means biasing one of the cylindrical memberstoward the other cylindrical member for drivingly connecting therotatable means to the lead screw through the clutch disc.

References Cited UNITED STATES PATENTS 1,565,754 12/1925 Orth 64291,860,750 5/1932 Riggs 6429 8 Naas 6429 Hardison 338-180 Krnse et a1338-143 Bourns et a1 338-183 Place 338-180 X Longerbach et a1. 338-183 XRICHARD M. WOOD, Primary Examiner.

10 I G. SMITH, Assistant Examiner.

1. IN A VARIABLE RESISTANCE CONTROL HAVING A HOUSING, A RESISTANCEELEMENT DISPOSED IN THE HOUSING, A LEAD SCREW ROTATABLY JOURNALED IN THEHOUSING, A CONTACTOR FOR MAKING WIPING CONTACT WITH THE RESISTANCEELEMENT, AND MEANS CONNECTING THE CONTACTOR TO THE LEAD SCREW FOR MOVINGTHE CONTACTOR INTERMEDIATE THE ENDS OF THE RESISTANCE ELEMENT AS THELEAD SCREW IS ROTATED THE IMPROVEMENT COMPRISING A PAIR OF ENGAGINGMEMBERS HAVING CLUTCH FACES, ONE OF THE ENGAGING MEMBERS BEING DRIVINGLYCONNECTED TO THE LEAD SCREW, THE OTHER OF THE ENGAGING MEMBERS BEINGROTATABLE EXTERNALLY OF THE HOUSING, AND ELECTRICALLY NONCONDUCTINGRESILIENT MEANS BIASING ONE OF THE ENGAGING MEMBERS INTO DRIVINGENGAGEMENT WITH THE OTHER ENGAGING MEMBER.